As police investigated why a gunman killed two utility workers in St. Louis before fatally shooting himself, workers from Laclede Gas Co. and other utilities cautiously returned to the field Friday.

Police say a man walked up to the workers Thursday and started shooting, then turned the gun on himself. "It does not appear words were exchanged," St. Louis police Capt. Mary Warnecke said.

Police believe the victims were picked at random. Laclede Gas and the electric company Ameren Missouri took workers off the city's streets Thursday as a precaution, and Missouri American Water and the Metropolitan St. Louis Sewer District removed workers from the immediate area of the shooting.

Workers were back in the field Friday. Laclede Gas spokeswoman Jenny Gobble said as employees reported for work they were given safety instructions, but she declined to elaborate.

Missouri American Water spokesman Brian Russell said meter readers and other workers who typically work alone were given the option of working in pairs. The utility will also consider long-term changes. "Our security team is going to review what happened after we get more details from police," Russell said.

Sewer district spokesman Lance LeComb said field workers were reminded "that if you see something amiss or that doesn't look right or makes you nervous, get someplace you feel safe and as quickly as possible call 911." Ameren said the company and workers "engaged in a healthy discussion about safety and maintaining situational awareness" before they were sent out Friday.

The shooting around 11:15 a.m. on St. Louis' western edge came two days after a man wanted in the slaying of a security guard gunned down three men, including a Pacific Gas & Electric Co. employee, in unprovoked attacks in downtown Fresno, California. Kori Ali Muhammad, 39, who is black, was arrested shortly after the rampage, and posts on what appeared to be his Facebook page discussed wanting to kill white people.

Police described the St. Louis shooter as black and both victims as white, but there was no indication the shooting was racially motivated. Warnecke said police "have no motive at this point in the investigation."

The names of the shooter and the men he killed have not been released. One of the slain workers was in his 20s and the other was in his 50s, authorities said.

Manyika McCoy told the St. Louis Post-Dispatch that the workers were connecting gas service to a home she was moving into - one was using a jackhammer and another was in a backhoe. She said she was at her mother's house nearby when she saw a man walking purposefully down the street toward the workers.

"I heard pop, pop," McCoy, 37, said.

The worker in the backhoe "was saying, 'Wait, wait,' and the guy just kept shooting at him," she said. The worker eventually collapsed in the street, she said.

Laclede, a natural gas distribution utility that serves the St. Louis area and portions of southeast Missouri, said it was "heartbroken" by the shooting.

St. Louis has one of the nation's highest homicide rates. The city recorded 188 killings in both 2015 and 2016 and had 45 this year through April 18, according to police.

New Mayor Lyda Krewson has said creating a safer city is among her top priorities. On Wednesday, her first full day in office, she announced that Police Chief Sam Dotson was retiring, though he will stay on as a consultant for one year.